Method of making power substrate assembly

ABSTRACT

A fixture is provided for facilitating the fabrication of a motor controller of the type including a power substrate module and a control circuit board mounted to and electrically coupled to the power substrate module via a plurality of conductors. The fixture is preferably a ring-like structure made of epoxy-fiberglass laminate. Apertures for engaging and holding the conductors are provided in the fixture at locations corresponding to conducting pads on the power substrate module. For fabrication, the power substrate module and the fixture are preformed and solder is disposed on the conducting pads of the module. During fabrication, the conductors are inserted into the apertures in the fixture and the fixture and conductors are positioned over the preformed power substrate module to bring the conductors into contact with the conducting pads. The fixture and power substrate module are then passed through a reflow oven to melt the solder and complete the connection of the conductors to the module. The fixture is left in place and connections to the conductors, such as by installing a control circuit board, may be completed in subsequent process or assembly steps.

BACKGROUND OF THE INVENTION

The present invention relates generally to a fixture used in the fabrication of a power substrate module. More particularly, the invention relates to a fixture that facilitates both the manufacture of power substrate modules for motor controllers and the assembly of such modules with other components in a motor controller package.

In the field of electronic motor controllers, it is commonplace to build a controller package as an assemblage of circuit boards, each supporting components and conducting paths for accomplishing various functions in the completed device. Such motor controllers generally include control logic circuitry and power components. The control logic circuitry, typically including programmable solid state circuits such as a programmable logic controller, monitor operating parameters of the motor and generate control signals for driving the motor in accordance with a preset control routine and various operator inputs. The power components typically include diode rectifying circuits for receiving AC power from a source and converting it to DC power, and power transistors or similar solid state switching devices, such as insulated gate bi-polar transistors (IGBT's), for converting the DC power to controlled AC signals for driving the motor based upon the control signals produced by the control circuitry.

In motor controllers of this type, the rectifying and inverting circuits are typically supported on a substrate or circuit board, often referred to as a power substrate module, typically along with other circuitry or components. Metallic pins are secured at specific locations on the power substrate module to provide connections for transmitting switching signals and AC power to and from these circuits. Once installed on the power substrate module, the conducting pins may be soldered or otherwise connected to other circuit boards, input or output terminals and the like. Thus, in the assembled controller, the conducting pins route power to the rectifying circuit and from the inverting circuit and provide signals causing the elements of the inverting circuit to open and close to produce the desired output signals for driving the motor.

To permit rapid assembly of the power substrate modules, special fixtures are typically made for holding the connecting pins at their appropriate locations in holes or on connection regions or pads on the surface of the power substrate. During assembly of each module, pins are placed in holes in a corresponding fixture and the fixture is brought into place over the substrate to locate the pins at their point of attachment. The fixture then follows the substrate through a reflow oven where solder at each of the attachment points of melted to secure the pins. The fixture is then removed from the pins and reused to assemble a following module in the same manner, while the assembled substrate continues to subsequent assembly stations. A number of identical fixtures are typically provided, permitting continuous assembly of identical modules during each production run.

While this assembly technique has generally proven reliable for the manufacture of power substrate modules, it is not without drawbacks. For example, because the fixtures must precisely and reliably locate the pin conductors through many assembly cycles, they must be specially machined for each substrate configuration. Moreover, because the fixtures undergo harsh thermal cycling as they follow substrates through the reflow oven, they are typically made of relatively costly metal alloys capable of withstanding such cycling without warping or otherwise deforming. In addition, once the fixture is removed from the conducting pins downstream of the reflow oven, the pins are left virtually unsupported, making them susceptible to bending during further processing, particularly during insertion into other circuit boards or components.

The present invention advantageously provides novel fixture that facilitates the connection of conductor pins to a power substrate module. The fixture is preferably made of a relatively inexpensive laminate material designed to be left in the assembly, thus eliminating the need for costly metal fixtures and providing support and protection for the conducting pins throughout the assembly process. The present invention also provides a method for fabricating a power substrate assembly that makes use of the novel fixture, as well as a motor controller power substrate module incorporating such a fixture.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, a fixture is provided for securing conducting pins to a power substrate module of the type including a rectifying circuit for converting alternating current power to direct current power, and inverting circuit for converting the direct current power to controlled alternating current power and conducting pads for transmitting power to and from the rectifying and inverting circuits. The fixture includes a substantially planar support having a plurality of apertures for permanently receiving and retaining the conducting pins over corresponding conducting pads on the power substrate module. The fixture is preferably made of an epoxy-fiberglass laminate material that is left on the conducting pins in the final assembly.

In accordance with another aspect of the invention, a power substrate assembly is provided for a motor controller. The assembly includes a power substrate module including rectifying and inverting circuits and conducting pads coupled to the rectifying and inverting circuits for receiving conductors. The assembly also includes a plurality of conductors secured to the conducting pads for transmitting power to and from the rectifying and inverting circuits and for transmitting control signals to the inverting circuit. The assembly further includes a fixture having apertures for receiving and supporting the conductors over corresponding conducting pads on the power substrate module.

In accordance with a further aspect of the invention, a method for fabricating a power substrate assembly is provided, including a preliminary step of forming a circuit on a power substrate module, the circuit including conducting pads for transmitting power to and from the circuit. A substantially planar fixture is also formed, having apertures for receiving a plurality of conductors. Solder material is deposited on the conducting pads, conductors are permanently inserted into the apertures in the fixture and the fixture is positioned over the power substrate module such that the conductors contact corresponding conducting pads. The solder material is then melted to connect the conductors to the power substrate module at the conducting pads.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which:

FIG. 1 is perspective view of a motor controller package in accordance with an exemplary embodiment of the present invention;

FIG. 2 is a top plan view of the motor controller illustrated in FIG. 1, showing the configuration of the input and output terminals with respect to the controller housing;

FIG. 3 is a diagrammatical illustration of the motor controller of FIG. 1, wherein various circuits comprising the controller and interconnections between the circuits are represented schematically;

FIG. 4 is a schematic illustration of circuits supported on a power substrate module of the motor controller of FIG. 1;

FIG. 5 is an exploded perspective of the circuit board and housing subassemblies of the motor controller shown in FIG. 1;

FIG. 6 is a perspective view of the power substrate module associated with the motor controller of FIG. 1 prior to assembly of the completed controller package;

FIG. 7 is a partial sectional view of a portion of the controller along section 7--7 of FIG. 2, illustrating the internal configuration of the assembled controller package; and

FIG. 8 is a detail view of a conductor disposed between the power substrate module and the control circuit board of the motor controller illustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings and referring to FIG. 1, an assembled motor controller or drive 10 includes a housing or enclosure 12 comprising a base 13 and a cover 14 containing power, drive and control circuitry as described in detail below. Enclosure 12 is preferably supported on a heat sink mount 16, including a cooling fan 18, for dissipating heat generated by operation of controller 10. Upon installation of controller 10, heat sink mount 16 is attached to a convenient location, such as within a wiring enclosure. Moreover, where a sufficiently heat dissipative surface is available for mounting controller 10, heat sink mount 16 may be removed.

As illustrated in FIG. 1, controller 10 includes a human interface 20 supported in cover 14. Interface 20 includes keys 22 for inputting desired parameter values, configuring controller 10 and verifying the controller configuration. Interface 20 also includes a visual display 24 for indicating to an operator various parameters and configuration codes input or accessed by operation of keys 22.

Controller 10 also includes a plurality of terminals, designated generally by the reference numeral 26. FIG. 2, which is a top plan view of controller 10 wherein cover 14 and a logic circuit board (described below) have been removed, more clearly shows these terminal locations. As shown in FIG. 2, ten such terminals are provided in a preferred embodiment of controller 10, including: incoming phase terminals 28, 30, 32; external brake resistor terminals 34, 36; outgoing phase terminals 38, 40, 42; and external capacitor terminals 44, 46. It will be noted that terminals 26 are provided on the outside of enclosure 12. This configuration facilitates coupling controller 10 to a source of AC power, to a motor to be controlled and to external brake resistors and capacitors by eliminating the need to remove a controller cover to access a terminal strip as on heretofore known controllers of this type. It will also be noted that incoming power terminals 28, 30, 32 are disposed on a first end of controller 10, while outgoing power terminals 38, 40, 42 are disposed on a second end opposite the first end. This arrangement also facilitates wiring of controller 10 to incoming and outgoing phase conductors by permitting controller 10 to be placed in an "in-line" orientation within a control cabinet or enclosure.

As illustrated diagrammatically in FIGS. 3 and 4, controller 10 includes a number of interconnected circuits within a unitary drive package. As shown in FIG. 3, controller 10 includes a power substrate module 48, a control circuit board 50, a logic circuit board 52 and a power supply circuit board 54. Each of these circuit boards supports various circuit components interconnected by conducting paths to form the functional circuits described below. The internal configurations of the individual circuits included on these circuit boards are of types generally known in the art, such as the circuits incorporated in the Bulletin 1305 motor drives available from the Allen-Bradley Company of Milwaukee, Wis.

Power substrate module 48 includes a rectifying circuit 56 and an inverting circuit 58 coupled by an internal DC bus 60 having a high voltage side 62 and a low voltage side 64. Upon installation of controller 10, rectifying circuit 56 is coupled to a source of AC power via incoming phase terminals 28, 30, 32 through suitable overload, overcurrent and short circuit protective devices such as fuses 66. Rectifying circuit 56 converts incoming AC power to DC power which is output on DC bus 60. Inverting circuit 58, in turn, converts the DC power from bus 60 to controlled AC power in response to drive command signals from a drive command circuit 76 as described below. This controlled AC power is applied to output terminals 38, 40, 42 to control the performance of a motor M coupled to the output terminals. In addition, a switching circuit 68 is coupled between high and low sides 62 and 64 of DC bus 60 for dissipating energy through an external brake resistor (not shown) coupled to terminals 34 and 36.

Control circuit board 50 includes circuits for monitoring certain operating parameters associated with motor M or controller 10, as well as for convening control signals from logic circuit board 52 to drive command signals for controlling the operation of inverting circuit 58. Thus, control circuit board 50 includes a current monitoring circuit 70 coupled to low side 64 of DC bus 60 for continuously detecting the current through bus 60. Similarly, a voltage monitoring circuit 74 is coupled to both high and low sides 62 and 64 of DC bus 60 and continuously detects the voltage across bus 60. Additional monitoring circuits, such as a temperature monitoring circuit, may also be included on control circuit board 50. Control circuit board 50 also supports a capacitive circuit 74 including capacitors coupled across DC bus 60 for storing energy during operation of controller 10. In addition, control circuit board 50 includes drive command circuit 76 which generates drive command signals for controlling inverting circuit 58.

Logic circuit board 52 includes a central processing circuit 78 configured to monitor operation of controller 10 and to generate control signals for regulating the performance of motor M. Central processing circuit 78 preferably includes a programmed microprocessor and, internal or external to the microprocessor, an analog-to-digital converter, memory circuitry and signal processing circuitry for storing and executing a predetermined cyclic control routine for driving motor M. Central processing circuit 78 is coupled to monitoring circuits 70 and 72 and receives signals representative of the DC bus current and voltage from the monitoring circuits. These signals are convened to digital values at a predetermined sampling interval for use in the cyclic control routine implemented by circuit 78. Central processing circuit 78 is also coupled to drive command circuit 76 and communicates control signals to drive command circuit 76 for driving motor M.

In addition to inputs from current and voltage monitoring circuits 70 and 72, logic circuit board 52 is typically coupled to a number of input and output channels, designated generally by reference numeral 79. Central processing circuit 78 uses channels 79 to receive incoming signals from interface 20 and from such external elements as start and stop circuits, reverse and jog switches, and the like, and to output display data for display 24. Input and output signals through 10. channels 79 are preferably communicated to central processing circuit 78 via an interface circuit 80 that includes opto-isolation for protecting control circuit 34 from power surges. Moreover, central processing circuit 78 receives input signals through one or more ports 84. For example, one such port 84 may be coupled to a potentiometer (not shown) for generating and supplying controller 10 with a target or desired drive signal frequency or motor output speed. Other ports 84 may be provided for various programming and control interface devices, such as a hand-held human interface module (not shown) or remote digital computer link. One or more output or monitoring ports 86 are preferably linked to central processing circuit 78, along with appropriate analog circuitry, for selectively monitoring the various operating parameters of controller 10, such as the desired and actual drive signal frequency or motor speed. Interface circuitry, designated generally at 82, is provided for isolating and conditioning the signals communicated to and from central processing circuit 78 through ports 84 and 86.

The principal functional elements of the circuits included in power substrate module 48 are illustrated schematically in FIG. 4. As shown, rectifying circuit 56 includes a plurality of diodes 88 coupled to input terminals 28, 30, 32 and to the high and low sides 62, 64 of DC bus 60 to form a full wave rectifier. Switching circuit 68 includes a switching device 90, such as an IGBT, and a diode 92. Brake resistor terminal 34 is coupled between switching device 90 and diode 92, while second brake resistor terminal 36 is coupled to the high voltage side 62 of DC bus 60. Switching device 90 is coupled to central processing circuit 78 through drive command circuit 76 and responds to switching signals from circuit 78 to permit current flow from the high voltage side 62 of DC bus 60, through an external resistor coupled to terminals 34 and 36 to the low voltage side 64 of DC bus 60. Thus, central processing circuit 78 can apply dynamic braking of motor M by actuation of switching device 90.

Inverting circuit 58 includes three pairs of switching devices, each pair including a high side device 95 and a low side device 94. Each high and low side switching device 95, 94 in turn includes an IGBT and a diode coupled between the transistor's emitter and collector. Moreover, in each pair of switching devices, the collector of the high side device 95 is coupled to the high side 62 of the DC bus. The emitter of the high side device 95 is coupled to the collector of the low side device 94 and the emitter of the low side device 94 is coupled to the low side 64 of the DC bus. Each switching device is coupled to a suitable power source, such as an 18 volt source originating on power supply board 54 or to a capacitor charge pump circuit (not shown), as well as to central processing circuit 78 through drive command circuit 76. Output terminals 38, 40 and 42 are coupled between the pairs of switching devices. Devices 94 and 95 are directed to conduct between the output terminals and the DC bus low side 64 and between the DC bus high side 62 and the output terminals, respectively, in response to drive control signals from drive command circuit 76. These drive control signals are based upon logic control signals from central processing circuit 78. Thus, central processing circuit 78 directs switching devices 94 and 95 to convert DC power from DC bus 60 to AC power that is output through terminals 38, 40 and 42.

In operation, controller 10 drives motor M as follows. The memory circuitry of central processing circuit 78 (or memory external to circuit 78) stores a cyclic control routine including features such as ramped acceleration, ramped deceleration, characteristic speed curves for particular applications, such as for pump drive applications, and so on. Such control routines are generally known in the art, such as the routines implemented in the Bulletin 1305 drives from the Allen-Bradley Company of Milwaukee, Wis. In addition, calibration values and operating parameters, such as desired speed or frequency may be input to central processing circuit 78 via a manual or computer networked interface, such as through input keys 22 and ports 84. Based upon these values and the preset control routine, central processing circuit 78 generates logic control signals and applies them to drive command circuit 76. Drive command circuit 76 in turn generates drive control signals and applies them to inverting circuit 58. The logic and drive control signals direct the switching devices of inverting circuit 58 to switch off and on so as to convert the DC power in DC bus 60 to AC power in the form of adjustable frequency pulse-width-modulated drive signals for driving motor M at a desired speed. This controlled AC power is applied to motor M via terminals 38, 40 and 42.

The preferred configuration of the various circuit boards included in controller 10 will now be described in greater detail, with particular reference to FIGS. 5 through 8. FIG. 5 is an exploded perspective view of the principal subassemblies of controller 10. As illustrated, logic circuit board 52, supporting interface circuit 80, is fitted within cover 14 above base 13. Base 13 includes a support surface 96 for supporting logic circuit board 52, as well as terminal bays 98 separated by partitions 100. Logic circuit board 52 is mounted on power supply board 54 and operationally coupled to power supply board 54 and to control circuit board 50 via a plurality of conducting pins 102 extending from the upper end of board 54.

Below support surface 96, control circuit board 50 supports power supply board 54 as well as two pairs of conductors 106 for transmitting electrical energy to capacitors 104 forming part of capacitive circuit 74. Because control circuit board 50 is located below support surface 96 and capacitors 104 are positioned above surface 96, capacitors 104 are mounted in the controller after insertion of control circuit board 50 in base 13. Control circuit board 50 is typically a hybrid type circuit board structure formed on an epoxy-fiberglass substrate material by generally known techniques. In addition to the various circuit components and conductive paths provided on control circuit board 50 to define the circuits described above, conductive pads are formed on board 50 for terminal conductors 108. During assembly of controller 10, terminal conductors 108 are inserted into pin connection apertures, shown generally at 110, in control circuit board 50 and are joined to board 50 by a wave soldering or similar operation.

Power substrate module 48 includes circuit components interconnected by conducting paths to form the functional circuits described above. Module 48 is preferably formed on a layered substrate material 112 having a lower aluminum base, an insulating layer overlying the base and a conductive layer overlying the insulating layer. During fabrication of module 48, the upper conductive layer of substrate material 112 is masked and etched by generally known techniques to form any conducting paths required between components as well as conducting pads 113 for transmitting AC power and drive signals to the module circuitry and controlled AC power from the circuitry. As best illustrated in FIGS. 6 through 8 and as discussed in greater detail below, power substrate module 48 is coupled to control circuit board 50 by conductors 114 that are anchored to conducting pads 113. A fixture 116 is positioned between power substrate module 48 and control circuit board 50 and includes conductor engaging apertures 117 through which conductors extend. Fixture 116 is preferably constructed in a ring-like configuration surrounding a central opening 118, permitting wire connections 120 to be installed between components of the module circuitry after attachment of conductors 114 as described below.

Following fabrication of the subassemblies illustrated in FIG. 5, controller I0 is assembled as follows. With power supply board 54 already mounted to control circuit board 50, power substrate module 48 is coupled to control circuit board 50 by inserting a portion of conductors 114 through corresponding pin connection apertures 110 on board 50 and soldering conductors 114 to conductive pads surrounding each aperture in a conventional manner. Module 48, board 50 and board 54 are then inserted into base 13. A power supply passage 122 and terminal conductor passages 124 (see FIG. 7) are formed in base 13 so that power supply board 54 and terminal conductors 108 may extend through base 13 as controller 10 is assembled. It should be noted that, although not specifically shown in the FIGURES, similar passages are provided for capacitor conductors 106 (shown in FIG. 5). Prior to fully engaging these boards in base 13, an adhesive is applied around the periphery of power substrate module 48. The board assembly is then pressed into base 13 and terminal conductors 108 are bent over terminal points 126 within each terminal bay 98 and between partitions 100. Terminal screws 128 are inserted into base 13 through terminal conductors 108. To complete assembly, capacitors 104 are mounted on conductors 106 (not shown in FIGS. 2 or 7), logic circuit board 52 is coupled to pins 102 on power supply board 54 and cover 14 placed over base 13 with interface circuit 80 positioned between interface 20 and logic circuit board 52. Thus assembled, power substrate module 48 is adhesively held within an attachment recess 130 within base 13.

Prior to final assembly of controller 10, a silicon-based thermal gel of a type generally known in the art is preferably added, such as through a hole 131 provided through support surface 96 of base 13. A sufficient quantity of thermal gel is forced into base 13 to cover power substrate module 48, fill the volume between module 48 and control circuit board 50 and cover board 50. The addition of this thermal gel allows the environments of power substrate module 48 and control circuit board 50 to be classified such that the component and conductive path spacing on module 48 and board 50 may be minimized in accordance with industry creepage and clearance specifications. Moreover, the separation of the higher voltage circuitry supported on power substrate module 48 from the lower voltage circuitry supported on control circuit board 50 places these two subassemblies in different classifications for the purposes of minimum creepage and clearance distances. As a result, the circuitry on board 50 can be more tightly packed than that on module 48 or than it could otherwise be packed if mounted on a common substrate with the circuitry on module 48.

The structure and assembly of power substrate module 48, conductors 114 and fixture 116 will now be described in greater detail with particular reference to FIGS. 6, 7 and 8. As best illustrated in FIG. 8, conductors 114 include a base portion 132 having a lower edge contacting surface 134. Extending at an angle from base portion 132 is a stress relief section 136. Stress relief section 136 joins an upper portion 138 having an upper shoulder 140. A fixture engaging portion 142 extends upwardly from shoulder 140 and conductor 114 terminates in a contacting pin joining a step 146 on the upper end of fixture engaging portion 142. While alternative configurations for conductors 114 may be envisioned, the foregoing structure facilitates connection of conductors 114 to power substrate module 48.

Assembly of power substrate module 48, conductors 114 and fixture 116 proceeds as follows. Power substrate module 48 is first prepared by conventional techniques, such as by etching its upper conductive layer and attaching circuit components at appropriate locations on the substrate material. A suitable solder material is deposited on each conducting pad 113 for later connection of conductors 114. Fixture 116 is formed separately, preferably from an epoxy-fiberglass laminate material. During formation of fixture 116, conductor engaging apertures 117 are pierced or otherwise formed at locations corresponding to the desired locations of conductors 114. Apertures 117 are preferably of similar geometry and slightly smaller than the fixture engaging portion of conductors 114, such that conductors 114 are press fitted into apertures 117 and solidly retained within fixture 116 during assembly. Conductors 114 are then pressed into apertures 117. The fixture is positioned over substrate module 48 with each conductor overlying the appropriate conducting pad 113; and the entire assembly is passed through a reflow oven to melt the solder on pads 113 and connect conductors 114 to module 48. This series of fabrication and assembly steps is preferably carded out on an automated assembly line of a type generally known in the art.

It will be noted that as conductors 114 are inserted into apertures 117, the upper shoulder 140 of each conductor 114 will contact the lower face of fixture 116, effectively limiting the insertion of conductor 114 into fixture 116 and properly locating conductors 114 at a uniform level with respect to fixture 116. Similarly, as control circuit board 50 is installed on contacting pins 144 as described above, steps 146 limit the downward movement of board 50 on pins 144 and support board 50 at a uniform level above module 48.

To complete power substrate module 48, prior to assembly with control circuit board 50, wire connections can be made between various components of the module circuitry, such as by wire bonding. To facilitate such later process steps, fixture 116 preferably does not completely cover module 48, but extends only over certain portions of module 48. Thus, fixture 116 may comprise one of more strips of material, an open ring or, in the presently preferred embodiment illustrated, a closed ring structure overlying only the periphery of module 48. 

I claim:
 1. A method for fabricating a power substrate assembly comprising the steps of:(a) forming a circuit on a power substrate module, the circuit including conducting pads for transmitting power to and from the circuit; (b) depositing solder material on the conducting pads; (c) forming a substantially planar fixture having apertures for receiving a plurality of conductors; (d) inserting conductors permanently into the apertures, a portion of the conductors extending through the fixtures portions of the fixture surrounding the apertures contacting the conductors to maintain the conductors in desired positions on the fixture; (e) positioning the fixture over the power substrate module to bring the conductors into contact with corresponding conducting pads; and (f) melting solder material to connect the conductors to the power substrate module at the conducting pads.
 2. The method of claim 1, wherein the conductors are press fitted into the fixture.
 3. The method of claim 1, wherein the fixture is formed of an epoxy-fiberglass laminate material.
 4. The method of claim 1, wherein the fixture has a closed ring configuration having a central opening, the apertures at least partially surrounding the central opening, whereby portions of the circuit of the power substrate module are accessible through the central opening.
 5. The method of claim 1, comprising the further step of wire bonding connections between portions of the circuit.
 6. A method for fabricating a power substrate assembly comprising the steps of:(a) forming a circuit on a power substrate module, the circuit including conducting pads for transmitting power to and from the circuit; (b) forming a fixture having apertures for receiving a plurality of conductors, locations of the apertures corresponding to locations of at least some of the conducting pads; (c) inserting conductors permanently into the apertures, a portion of the conductors extending through the fixture, portions of the fixture surrounding the apertures contacting the conductors to retain the conductors thereon; (d) positioning the fixture over the power substrate module to bring the conductors into contact with corresponding conducting pads; and (e) electrically coupling the conductors to the power substrate module at the conducting pads.
 7. The method of claim 6, wherein the conductors are press fitted into the fixture.
 8. The method of claim 6, wherein the fixture is formed of an epoxy-fiberglass laminate material.
 9. The method of claim 6, wherein the fixture has a ring configuration having a central opening, the apertures at least partially surrounding the central opening, whereby portions of the circuit of the power substrate module are accessible through the central opening.
 10. The method of claim 6, comprising the further step of wire bonding connections between portions of the circuit.
 11. The method of claim 6, wherein the conductors include abutment surfaces abutting the fixture when the conductors are installed in the apertures.
 12. A method for fabricating a power substrate assembly comprising the steps of:(a) forming a circuit on a power substrate module, the circuit including conducting pads for transmitting power to and from the circuit; (b) forming a substantially ring-shaped, planar fixture of an epoxy-fiberglass laminate material having apertures for receiving a plurality of conductors; (c) inserting conductors permanently into the apertures; (d) positioning the fixture over the power substrate module to bring the conductors into contact with corresponding conducting pads; and (e) soldering the conductors to the pads.
 13. The method of claim 12, wherein the conductors are press fitted into the fixture.
 14. The method of claim 12, wherein portions of the circuit of the power substrate module are accessible through the central opening of the fixture.
 15. The method of claim 12, comprising the further step of wire bonding connections between portions of the circuit. 